spinal cord & spinal nerves eng -...

Central nervous system.

Spinal cord and spinal nerves

1. Central nervous system – gross subdivisions2. Spinal cord – embryogenesis and external structure3. Internal structure of the spinal cord4. Grey matter – nuclei and laminae5. White matter – nerve fiber tracts6. Reflex apparatus of the spinal cord7. Formation and general organization of the spinal nerves8. Dorsal and ventral rami of the spinal nerves – plexuses

Prof. Dr. Nikolai Lazarov 2

Classification of the nervous system


� origin: neuroectodermal� caudal part of the neural tube

� begin of formation: 3rd week� developmental stages: basal plate and alar plate

� neural plate� neural groove� neural tube� nerve crest

� closure of posterior neuropore: 4th week� histogenesis – zones in the wall:

� marginal layer � white matter

� intermediate (mantle) layer � grey matter

� ventricular (ependymal) layer � central canal

Embryogenesis of the spinal cordSpinal cord


Topographic location, size and extent� topography and levels – in the vertebral canal

� fetal life – the entire length of vertebral canal� at birth – near the level L3 vertebra� adult – upper ⅔ of vertebral canal (L1-L2)

� average length:� ♂ – 45 cm long� ♀ – 42-43 cm

� diameter ~ 1-1.5 cm (out of enlargements)� weight ~ 35 g (2% of the CNS)� shape – round to oval (cylindrical)� terminal part:

� conus medullaris� filum terminale internum

(cranial 15 cm) – S2� filum terminale externum

(final 5 cm) – Co2� cauda equina – collection of

lumbar and sacral spinal nerve roots

Spinal cord


� cervical enlargement, intumescentia cervicalis:� spinal segments (C4-Th1)

� vertebral levels (C4-Th1)

� provides upper limb innervation (brachial plexus)

� lumbosacral enlargement,intumescentia lumbosacralis:� spinal segments (L2-S3)

� vertebral levels (Th9-Th12)

� segmental innervation of lower limb (lumbosacral plexus)

Macroscopic anatomy – enlargementsSpinal cord


� Two symmetrical halves :� divided by two external longitudinal grooves:

� a deeper anterior median fissure� a shallower posterior median sulcus (less prominent)

� joined by a commissural band of nervous tissue

External surface structureSpinal cord


Anterior median fissure

� average depth ~ 3 mm:� deeper at more caudal levels

� roof:�a reticulum of pia mater

� floor:�a lamina of nerve fibers,

anterior white commisure

� anterior spinal artery� anterolateral suclus –

ventral nerve root

Spinal cord


Posterior median septum� average depth ~ 4-6 mm:

�diminishing caudally� neuroglial partition:

� reaching the gray matter� posterolateral suclus –

dorsal nerve root

Spinal cord


� 31 segments:�8 cervical�12 thoracic�5 lumbar �5 sacral �1 coccygeal

� segment ≠ vertebra:� growth of the vertebral column

exceeds that of the spinal cord� all segments terminate above

level L1/L2 � cauda equina� vary in diameter and length

Spinal cord

Segmental structure


� grey matter, substantia grisea� butterfly-like or H-shaped

� white matter, substantia alba� vary in diameter and length

at different levels

Internal structure of the spinal cordSpinal cord


� composition:� neuronal perikarya� dendrites with their synapses� glial supporting cells� blood vessels

� anterior (ventral) column:� cornu anterius (columna anterior)

� posterior (dorsal) column: � cornu posterius

(columna posterior)� lateral column:

� cornu laterale – Th1-L2; S2-S4(columna intermedia)

� central canal:� canalis centralis � liquor cerebrospinalis� substantia gelatinosa centralis

� grey commissure: � commissura grisea

Spinal cordGrey matter, substantia grisea


Spinal cord

� posterior column (dorsal horn): � apex, caput, cervix, basis� projection neurons (neurocyti funiculares)

and interneurons (neurocyti interni)

� lateral column (intermediolateral horn):� visceromotor neurons

� parasympathetic� sympathetic

� anterior column (ventral horn):� motor neurons (neurocyti radiculares)

� large alpha motoneurons (ACh)

� small gamma motoneurons (ACh)

� Renshaw cells (Gly)(inhibitory interneurons)

General structure of the grey matter


dorsal horn: 4 nuclei�dorsomarginal nucleus (zona spongiosa)�substantia gelatinosa of Rolando�nucleus proprius�nucleus dorsalis (thoracicus) of Clarke-Stilling

lateral horn: 2 nuclei�sympathetic: intermediolateral nucleus (Th1-L2)

�parasympathetic: intermediomedial nucleus (S2-S4)

�spinal reticular nucleus

ventral horn: 5 nuclei�medial group

�ventromedial nucleus�dorsomedial nucleus

�lateral group�ventrolateral nucleus�central nucleus�dorsolateral nucleus

Grey matter – nerve cell groupsSpinal cord

� receive pain impulses


10 distinct cellular laminae of Rexed:�I-VI: dorsal horn�VII: intermediate zone and lateral horn�VIII-IX: ventral horn�X: central canal + substantia gelatinosa (of Rolando)

Spinal cordGrey matter – laminar architecture


Spinal cordGrey matter – functional organization

� different sensations – different neurons (the law of Bell and Magendie)

� the theory of nerve components:� dorsal horn mediates sensation

� general somatic afferents� general visceral afferents (GVA)

� ventral horn mediates motor function� general somatic efferents (GSE)

for the ventral roots

� intermediate horn� receives GVA axons� originates GVE axons

� the perikarya in various nuclei differ in size, shape and connections

� nuclear groups in grey columns vary in longitudinal extent

Longitudinal extent of the nuclei


� posterior funiculus: funiculus dorsalis (posterior)

� lateral funiculus: funiculus lateralis

� anterior funiculus: funiculus ventralis (anterior)

� composition: ■ 3 columns (funiculi) – ascending and descending tracts� nerve fibers� glia� blood vessels

White matter compositionSpinal cord


� Ascending pathways:

� Descending pathways:

1. Fasciculusinterfascicularis, s. semilunaris(of Schultze) =Interfascicular fasciculus

2. Fasciculus septomarginalis(of Flechsig)

1. Fasciculus gracilis (of Goll)2. Fasciculus cuneatus (of Burdach)

Dorsal column tractsSpinal cord


Fasciculus gracilis

� present at all spinal levels

� terminates somatotopically upon the nucleus gracilis

� subserves superficial sensitivity (discriminative modalities) and deep sensitivity (kinesthesia) from the lower part of the trunk and from the leg

� interruption of this tract causes

� loss of position sense resulting in posterior column ‘sensory ataxia’

Spinal cord

1. gracile fascicle , synonym: Goll’s column�medial part of the posterior funiculus


Fasciculus cuneatus

� first appear at about Th6

� contains long ascending branches of the upper six thoracic and all cervical dorsal roots

� deep sensitivity (proprioception) from the upper part of the trunk and from the arm

� superficial sensitivity – touch, pressure and vibration

� interruption of this tract causes� loss of position sense resulting in

‘sensory ataxia’

2. cuneate fascicle , synonym: Burdach’s column� lateral part of the posterior funiculus


Posterior funiculus� Descending tracts:

1. Interfascicular fascilulus, semilunar tract(comma tract of Schultze)� in the medial part of

the cuneate tract� extending through

cervical and upper thoracic levels

2. Septomarginal tract(oval field of Flechsig)� bordering the posterior

median septum� in lower thoracic

segments� propriospinal fibers

� Intersegmental tracts:� Posterior

intersegmental tract

Spinal cord


1. Dorsal spinocerebellar tract (of Flechsig)2. Ventral spinocerebellar tract (of Gowers)3. Lateral spinothalamic tract (of Edinger)4. Spinotectal tract5. Spino-olivary tract6. Spinoreticular fibers7. Dorsolateral tract (of Lissauer)

� Ascending tracts:

� Descending tracts:1. Lateral corticospinal tract2. Rubrospinal tract3. Tectospinal tract4. Lateral reticulospinal tract5. Olivospinal tract (of Helweg) – only in animals

Spinal cord

Lateral funiculus

� Intersegmental tracts:1. Lateral intersegmental tract


1. Anterior spinothalamic tract

1. Anterior corticospinal tract (bundle of Türk)

2. Reticulospinal tract

3. Vestibulospinal tract (medial and lateral)

4. Medial longitudinal fasciculus

5. Interstitiospinal tract

6. Solitariospinal tract (of Cajal)

Spinal cord

Anterior funiculus

� Ascending tracts:

� Descending tracts:

� Intersegmental tracts:1. Anterior intersegmental tract


Functional topography of pathwaysSpinal cord

Posterior (dorsal funiculi) columns :�proprioception (position sense)

�vibratory sense

�discriminative touch


Spinal cordReflex arcs of the spinal cord

‘Final common path(way)’ (of Sherrington)

� reflex arc – the neural pathway that mediates a reflex action

� two types of reflex arcs:� autonomic reflex arc (affecting inner organs)� somatic reflex arc (affecting muscles)

� monosynaptic vs. polysynapticreflex arcs


Spinal cordPatellar Reflex Testing


� 31 pairs of segmentally arranged nerves:� 8 cervical – C1-C8� 12 thoracic – Th1-Th12� 5 lumbar – L1-L5� 5 sacral – S1-S5� 1 coccygeal – Co1

� corresponds to a pair of embryonic somites� emerges through the intervertebral foramen� mixed spinal nerve (common nerve trunk)

� topographic relationships between spinal nerves, segments and vertebrae

General organization of the spinal nervesSpinal nerves


� ventral (motor) root:� axons of neurons in anterior and lateral grey columns� motor and autonomic (sympathetic and parasympathetic)

� dorsal (sensory) root:� central processes of the dorsal ganglion cells� convey somatic and visceral sensory information

Spinal nerve formationSpinal nerves


� spindle-shaped aggregations on the dorsal roots – dorsal root ganglion� (pseudo)unipolar neurons – ovoid or spherical

(primary afferent neurons)� satellite cells (capsular cells, amphicytes)� Schwann cells and blood vessels

� embryonic origin – neural crest cells� location – in intervertebral foramina� axons (afferents) – proximal and

distal processes� functional modalities:

� mechanoreception� nociception� proprioception

Spinal ganglionSpinal nerves


� Spinal nerve functional components:� somatic components – efferent and afferent fibers

� visceral components – sympathetic or parasympathetic

� Spinal nerve branches:� meningeal branch – at all vertebral levels

(recurrent meningeal nerve)� white ramus communicans – myelinated preganglionic fibers

� all thoracic and L1-L2 to corresponding sympathetic ganglion� S2-S4 nerves to the parasympathetic pelvic plexus

� grey ramus communicans – unmyelinated postganglionic fibers� from paravertebral sympathetic ganglia

� ventral (anterior) ramus – thicker� ventrolateral muscles� skin of the trunk and extremities

� dorsal (posterior) ramus – thinner� intrinsic dorsal muscles of the back and neck� overlying skin from vertex to coccyx

Spinal nerve trunksSpinal nerves


Dorsal rami of the spinal nervesSpinal nerves

� divide into medial and lateral branches (exception C1)

� have a typical segmental distribution� cervical dorsal rami:

� suboccipital nerve (C1) – purely motor� greater occipital nerve (C2) – mixed� C3 medial cutaneous branch, third occipital nerve

� thoracic dorsal rami:� Th1-Th6 – medial (mixed) and lateral (motor) branch� Th7-Th12 – medial (motor) and lateral (mixed)

� lumbar dorsal rami:� L1-L3 lateral cutaneous branches – superior clunial nerves

� sacral dorsal rami:� S1-S3 lateral cutaneous branches – medial clunial nerves


Ventral rami of the spinal nervesSpinal nerves

� Thoracic ventral rami – 12 pairs:� segmental distribution –

intercostal nerves� Th12 – subcostal nerve� anterior cutaneous branches� lateral cutaneous branches


� Formation and segmental origin:� ventral rami of C1-C4 nerves

� Branches:� superficial (sensory) branches:

� lesser occipital nerve, n. occipitalis minor

� great auricular nerve,n. auricularis magnus

� transverse colli nerve,n. transversus colli

� supraclavicular nerves,nn. supraclaviculares

� deep (motor) branches:� muscular branches, rr. musculares� inferior root of the ansa cervicalis,

radix inferior ansae cervicalis� trapezius root, ramus trapezius� sternocleidomastoid root, r. sternocleidomastoideus

� phrenic nerve, n. phrenicus

Cervical plexus, plexus cervicalis


Brachial plexus, plexus brachialis

� Formation and segmental origin:� ventral rami of C5-C8, Th1 nerves

� Three primary trunks:� superior (upper) trunk – C5-C6� middle trunk – C7� inferior (lower) trunk – C8-Th1

� Divisions:� posterior division

� posterior cord

� anterior� lateral cord� medial cord


Brachial plexus, plexus brachialis� Main branches:

� supraclavicular part:� dorsal scapular nerve,

n. dorsalis scapulae� long thoracic nerve,

n. thoracicus longus� nerve to the subclavius,

n. subclavius� suprascapular nerve,

n. suprascapularis� infraclavicular part:

� lateral cord, fasciculus lateralis:• musculocutaneous nerve, n. musculocutaneus• lateral root of median, radix lateralis n. mediani

� medial cord, fasciculus medialis:• medial root of median, radix medialis n. mediani• ulnar nerve, n. ulnaris• medial cutaneous of arm, n. cutaneus brachii medialis• medial cutaneous of forearm,

n. cutaneus antebrachii medialis� posterior cord, fasciculus posterior:

• axillary nerve, n. axillaris• radial nerve, n. radialis


Brachial plexus, plexus brachialis

� Brachial distribution of:� musculocutaneous nerve� median nerve� ulnar nerve� radial nerve

� Forearm innervation:� median nerve� ulnar nerve� radial nerve

� Hand innervation:� median nerve� ulnar nerve


Muscle innervation of the upper limb

� Muscular branches of:� median nerve� ulnar nerve� radial nerve


Cutaneous innervation of the upper limb


Peripheral neuropathies

� Radial nerve palsy, wrist drop (Saturday night palsy)

� Ulnar nerve palsy, ‘claw hand’ handlebar palsy – cyclist’s hands

� Median nerve palsy,‘accoucheur's hand’

median neuropathy (Carpal tunnel syndrome)–


� Lumbar plexus, plexus lumbalis:� formation and segmental origin:

�ventral rami of Th12, L1-L4 nerves

Lumbosacral plexus, plexus lumbosacralis

� Sacral plexus, plexus sacralis:� formation and segmental origin:

�ventral rami of L5, S1-S5, Co1 nerves

� Coccygeal plexus, plexus coccygeus:� ventral rami of S5,Co1


Lumbar plexus, plexus lumbalis

� Branches:� muscular branches,

rr. musculares� purely sensory branch:

� lateral femoral cutaneous nerve, n. cutaneus femoris lateralis

� sensorimotor branches:� iliohypogastric nerve,

n. iliohypogastricus� ilioinguinal nerve,

n. ilioinguinalis� genitofemoral nerve,

n. genitofemoralis� obturator nerve,

n. obturatorius� femoral nerve,

n. femoralis


Femoral nerve, n. femoralis

� passes through lacuna musculorum

� branches – L2-L4:

� muscular branches, rr. musculares:

� iliopsoas

� pectineus

� sartorius

� extensor muscles of the knee –

quadriceps femoris

� sensory branches:

� anterior femoral cutaneous nerve

� saphenous nerve


Sacral plexus, plexus sacralis� Branches:

� motor branches:� muscular branches,

rr. musculares� superior gluteal nerve,

n. gluteus superior� inferior gluteal nerve,

n. gluteus inferior� purely sensory branch:

� posterior femoral cutaneous nerven. cutaneus femoris posterior

� sensorimotor branches:� pudendal nerve,

n. pudendus� coccygeal nerve,

n. coccygeus� sciatic nerve,

n. ischiadicus� visceral branch:

� pelvic splanchnic nerve, nervus erigens


Sciatic nerve, n. ischiadicus� passes through foramen infrapiriforme� Main branches:

� tibial nerve, n. tibialis:

� articular branches

� muscular branches

� sural nerve

� medial and lateral calcaneal

� medial and lateral plantar nerves

� common peroneal nerve, n. peroneus communis:

� superficial peroneal nerve (musculocutaneous)

� deep peroneal nerve (anterior tibial nerve)


Saturday night palsy

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Spinal nerves

spinal cord & spinal nerves eng -...

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